Automobiles and trucks have exterior finishes for several well known reasons. First, such finishes provide barrier protection against corrosion. Second, consumers prefer an exterior finish having an attractive aesthetic finish, including high gloss and excellent DOI (distinctness of image).
The exterior surface of a typical automobile or truck has several layers of finishes or coatings. If the substrate is steel, it typically is first coated with an inorganic rust-proofing zinc or iron phosphate layer over which is provided a primer which can be an electrocoated primer or a repair primer. Optionally, a primer surfacer can be applied to provide for better appearance and/or improved adhesion. A pigmented basecoat or color coat is next applied over the primer. A typical basecoat or color coat contains a mixture of pigments, which may include metallic flake pigments in the case of a metallic finish. In order to protect and preserve the aesthetic qualities of the finish on the vehicle, it is well known to provide a clear (unpigmented) topcoat or clear coat over the colored (pigmented) basecoat, so that the basecoat remains unaffected even on prolonged exposure to the environment or weathering.
Aqueous coating compositions of a self-stabilized latex of a graft copolymer which can be pigmented and used as a basecoat in a clear coat/base coat finish for automobile and trucks is shown in WO Patent application 95/3229 published Nov. 30, 1995. While the coating composition disclosed therein are adequate, improvement is need for chip resistance of the finish formed from such coatings. Chipping of an automotive finish occurs when debris strikes the automobile while driving and this debris is usually in the form of stones, gravel and or sand. The coating composition of this invention provides a finish with improved chip resistance in comparison to those of the prior art.